Pleated filter element having an additional structure

ABSTRACT

A filter element comprising a pleated filter mat (3), the terminal axial ends (7, 8) of which are connected by an end cap (9, 11) and which includes a main structural layer (15) having filtering properties and at least one first additional structural layer and a second additional structural layer (17, 19), the surface area of each of said additional structural layer (17, 19) being smaller than the surface area of the main structural layer (15), is characterized in that the axial ends (12, 14) of one additional structural layer (17) is located at n an axial distance from the axial ends (16, 18) of the other additional structural layer (19) on the filter mat (3).

The invention concerns a filter element comprising a pleated filter mat, wherein each of the ends of said filter mat is attached to an end cap and which is provided with a main structural layer with filtering properties as well as at least a first and a second additional structural layer, wherein the surface area of each of said additional structural layers is smaller than the surface area of the main structural layer. Moreover, the invention concerns a method for the manufacture of a filter element of this kind.

A filter element of this kind is known from the document DE 10 2004 061 078 A1. The additional structural layers provided in this solution, which extend with a different surface area from one end of the main structural layer at which they are embedded together with the main structural layer in an end cap, have the purpose of optimizing the filtering properties of the filter element. To this end the main structural layer in the known solution may be designed as the main filtration layer with regard to fluid permeability in such a way that large amounts of fluid are able to pass through with a reasonable level of dirt absorption capacity whilst the additional structural layers as pre-filters have a greater filter fineness. This improves the operating performance of the filter element in that respect that with a so-called cold-start of the connected hydraulics plant, when the fluid to be filtered is still cold and has a correspondingly high viscosity, the main filter poses little flow resistance, and the pre-filter together with parts of the main filter ensure the desired dirt absorption capacity.

Based upon said prior art it is the object of the invention to provide a filter element of the kind described at the outset which, whilst retaining the described advantages of the prior art, provides stabilization of the pleats of the filter mat through additional structural layers against forces that act during filter operation.

This object is met according to the invention through a filter element that exhibits the characteristics of claim 1 in its entirety.

According to the characterizing part of claim 1 a significant feature of the invention lies in the fact that the axial ends of the one additional structural layer is located at an axial distance from the axial ends of the respective other additional structural layer. Due to the fact that, contrary to the known solution in which all additional structural layers are embedded together with the main structural layer at a common end into an end cap, in the invention the structural layers are disposed at completely separate positions from each other along the axial length of the filter mat, it is possible to achieve pleat stabilization in selected areas through additional structural layers that are assigned to certain areas.

In a particularly advantageous manner the arrangement may be such that two additional structural layers are provided and that at each of the two end caps an additional structural layer each is welded at one end together with the respective end of the main structural layer into the corresponding end cap. This not only provides increased stability at both end caps through a concentration of material whilst the sections between the end caps, which are free of additional structural layers, have a correspondingly higher flexibility with increased free space between the pleats of the filter mat. Furthermore, said concentration of material ensures a particularly solid embedding of the filter mat in the end caps since, during manufacture of the filter element, more molten material is available during the welding process at the hot end cap, which safely encloses the filter mat. The danger that a bypass is formed at the filter element is thus greatly reduced. Since the material concentration, which is required for securely embedding the filter mat into the end cap. does not extend along the entire length of the filter element, the overall volume of the filter mat is reduced whilst maintaining the same pleat stability, which in turn leaves more space between the pleats for retaining contaminant particles. Moreover, the thus flexible filter mat is able to provide additional flow-exposed surface area due to its inflation at already very low differential pressure.

In advantageous exemplary embodiments the filter mat may be provided with a third stabilizing additional structural layer, the ends of which are located at an axial distance from the first as well as from the second structural layer, which are attached to an end cap. Through a third additional structural layer, which is disposed in this manner, a spacer is provided for longer filter elements through the third additional structural layer, which is, for example, disposed in the center. Said spacer stabilizes the pleat geometry along the entire length of the filter element.

The additional structural layers may be provided as stabilizing filler material only, without filtering properties, but may also have filtering properties that are preferably different to the filtering properties of the main structural layer that forms the main filter, and are chosen such that optimal filtering properties are achieved.

The additional structural layers are preferably pleated and are preferably folded with the same type and number of pleats together with the main structural layer, wherein the main structural layer as well as the additional structural layers may comprised of multiple layers.

The additional structural layers may be folded into the filter mat as an external or an internal layer. Moreover, the additional structural layers may be folded into the fitter mat at the upstream or downstream side, and the axial length of the additional structural layers may vary.

According to claim 11, an object of the invention is also a method for the manufacture of a filter element according to one of the claims 1 to 10. As described in the characterizing part of claim 11, a filter mat consisting of multiple layers is folded in one processing step from a preferably multi-layered main structural layer with filtering properties together with at least one further additional structural layer that consists of stabilizing material. Moreover, the fitter mat created in this manner is formed into a hollow body that is circumferentially closed along a longitudinal seam. Said longitudinal seam may be provided by a welding seam or an adhesive connection. The ends of the hollow body, which consist of the main structural layer and at least one additional structural layer, are then enclosed with end caps through welding or by adhesive means. The material of the additional structural layers together with the components of the main structural layer may provide a volume of molten material during the welding process to the end cap.

The invention will now be explained in detail by way of exemplary embodiments shown in the drawing.

Shown are in:

FIG. 1 a perspective view of an exemplary embodiment of the filter element according to the invention;

FIG. 2 a perspective view of a section of the length of the filter mat of the exemplary embodiment of the filter element shown in a stretched-out state and shown enlarged compared to that of FIG. 1;

FIG. 3 a perspective view of an end section of the filter mat of the exemplary embodiment, formed into a hollow body, prior to insertion into an end cap;

FIG. 4 a depiction of the filter mat inserted into the end cap corresponding to that of FIG. 3; and

FIG. 5 a schematically simplified perspective view of a second exemplary embodiment of the filter element according to the invention.

FIG. 1 depicts a filter element according to a first exemplary embodiment of the invention, designated overall with 1. In a manner usual for circular-cylindrical filter elements, the filter medium is made from a pleated filter mat 3, which is formed into a hollow body that is closed circumferentially through a longitudinal seam 5, implemented through a welding seam or an adhesive connection. The filter mat 3, of which FIG. 2 shows a section of the length in a stretched-out state, is welded or glued into an end cap 9 and 11 at both axial ends 7 and 8 respectively, of which only one end is visible and designated with 7 in FIG. 3, wherein said end caps 9 and 11 form a rim for the end of the filter mat 3, as is common practice with filter elements of this kind. The end cap 9, which is shown at the top in FIG. 1 and is also shown in FIGS. 3 and 4, is made in form of a closed cap, whereas the lower end cap 11 is provided with a central passage 13 to the inner filter cavity, which is surrounded by the filter mat 3. When the flow travels through the filter mat 3 from outside to inside during filter operation, the inner hollow filter section may be provided with a fluid-permeable supporting tube (not shown in FIG. 1), which is in contact with the inside of filter mat 3. The end caps 9 and 11 are made from a plastic material that is suitable for a welding process, onto which components of the items to be joined will melt when end cap 9, 11 is heated up.

FIG. 2 dearly shows the design of the filter mat 3. From axial end 7 to axial end 8 it is provided with a continuous main structural layer 15, as well as a first additional structural layer 17 and a second additional structural layer 19, each of which is shorter than the main structural layer 15. During the folding process in the manufacture of filter mat 3, said additional structural layers 17 and 19 are folded in so that they start from an end 7 or 8 each. More precisely, the additional structural layer 17 starts with its end 12 at the end 7 of the filter material 3, and the additional structural layer 19 starts with its end 18 at the end 8 of the filter material 3, wherein the length of each structural layer 17, 19 is only a fraction of the axial length of the main structural layer 15. In practical application, as shown in FIG. 1, the axial length of each additional structural layer 17, 19 is approximately 1/15 of the length of the main structural layer 15. As is common for these kinds of filter materials, the main structural layer 15 is comprised of multiple layers, wherein a supporting fabric may be provided as a first layer, a protection fleece as a second layer, a main fleece as third layer, and wherein further layers may be provided as protection fleece and supporting fabric, wherein said supporting fabric may consist of a plastic mesh or a woven plastic if the mat structure is free of metal. The additional structural layers 17, 19 may consist of a fluid-impermeable plastic material, which forms a stabilizing filler between pleats 21 and consist of a material that is suitable for a welding process. Nevertheless, the additional structural layers 17, 19 may, just like components of the main structural layer 15, also consist of a plastic material with filtering properties, which supplies melt material for the welding process.

The additional structural layers 17, 19 may, during manufacture of the filter mat 3, be folded in together in such a way that the additional structural layers 17, 19 are in contact with the outside of the filter mat 3, as is apparent from FIG. 2, so that the each other facing ends 14 and 16 of the additional structural layers 17 and 19 are visible, as shown in FIG. 2. The additional structural layers 17, 19 may also be folded in on the inside between individual layers of the main structural layer 15, or on the inside or at the back (not visible in FIG. 2). The additional structural layers 17, 19 may advantageously consist of a material that hardens during the folding process or hardens subsequently after application of heat. For example a prepreg material may be used, preferably consisting of a base material of carbon fiber or glass fiber, wherein the associated quantity of resin is matched so that the material of the additional structural layers 17, 19 cures during the folding process or hardens in a further processing step through application of heat. Through the concentration of material at the endcaps 9, 11, caused by the additional structural layers 17, 19, a particularly secure embedding of the filter mat 3 into the end caps 9, 11 is ensured since for the welding process, which occurs through the heating up of the end caps 9, 11, more molten material is available which securely encloses the filter mat 3. Since the material concentration is only present in certain sections there is no significant increase in the overall material concentration of filter mat 3, hence there remains space between the pleats 21 to retain contaminant particles. Moreover, the filter mat 3 remains flexible. The greater flexibility in the sections without additional structural layers 17, 19 is advantageous for filter mat 3, for example in reverse pressure pulses during operation because the flexible filter mat 3 is able to expand and thus provide a greater amount of free, flow-exposed surface area.

FIG. 5 depicts a further exemplary embodiment of the filter element 1 according to the invention. This concerns an embodiment of comparatively long construction. In addition to the additional structural layers 17, 19, which extend from the end caps 9 and 11, a third additional structural layer 23 is provided in this example. In the example shown, said layer is folded centrally into the web of filter mat 3, at a distance to the additional structural layers 17, 19, so that it is placed on the outside of the main structural layer 15, like the additional structural layers 17, 19, and that the ends 25 and 27 of the additional structural layer 23 are located at a distance from the adjacent ends 14 and 16 of the additional structural layer 17 and 19 respectively. Said third additional structural layer 23 consists of filler material which, like the material of the other additional structural layers 17, 19, cures or may cure during the folding process, and serves as stabilizing spacer that keeps the space between the pleats 21 open over the length of the element. Just like the two other additional structural layers 17 and 19, the third additional structural layer 23 may also be provided with filtering properties or be made of fluid-impermeable filler. 

1. A filter element comprising a pleated filter mat (3), the axial ends (7, 8) of which are each attached to an end cap (9, 11), which is provided with a main structural layer (15) with filtering properties as well as at least a first and a second additional structural layer (17, 19), which have a surface area each that is smaller than the surface area of the main structural layer (15), characterized in that the axial ends (12, 14) of the one additional structural layer (17) on the filter mat (3) are at an axial distance from the axial ends (16, 18) of the respective other additional structural layer (19).
 2. The filter element according to claim 1, characterized in that two structural layers (17, 19) are provided and that at each of the two end caps (9, 11) an additional structural layer (17, 19) each is welded with one end (12, 18) together with the associated end (7, 8) of the main structural layer (15) into the respective end cap (9, 11).
 3. The filter element according to claim 1, characterized in that the filter mat (3) is provided with a third stabilizing additional structural layer (23), the ends (25, 27) of which are disposed at an axial distance from the first (17) as well as the second structural layer (19) that are attached to an end cap (9, 11).
 4. The filter element according to claim 1, characterized in that the additional structural layers (17, 19, 23) are provided without filtering properties.
 5. The filter element according to claim 1, characterized in that the additional structural layers (17, 19, 23) are provided with filtering properties.
 6. The filter element according to claim 1, characterized in that the additional structural layers (17, 19, 23) are pleated, having preferably the same type and amount of pleats (21) and are folded together with the main structural layer (15) into the filter mat (3).
 7. The filter element according to claim 1, characterized in that the main structural layer (15) and/or the additional structural layers (17, 19, 23) are made of multiple layers.
 8. The filter element according to claim 1, characterized in that the additional structural layers (17, 19, 23) are folded into the filter mat (3) either as outer or as inner layers.
 9. The filter element according to claim 1, characterized in that the additional structural layers (17, 19, 23) are folded into the filter mat (3) either on the upstream side or on the downstream side.
 10. The filter element according to claim 1, characterized in that the axial length of the additional structural layers (17, 19, 23) is variable.
 11. A method for the manufacture of a filter element according to claim 1, characterized in that a preferably multiple-layered filter mat (3), consisting preferably of a multi-layered main structural layer (15) with filtering properties, is folded together with at least one further additional structural layer (17, 19, 23), that the filter mat (3) is formed into a circumferentially closed, hollow body along a longitudinal seam (5), and that the ends (7, 8) of the hollow body, which consist of main structural layer (15) and at least one additional structural layer (17, 19), are connected through welding or adhesive joining. 